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  1. #51
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    Quote Originally Posted by HHMTB
    I was surprised when I took this thing fully apart for the pictures that there seems to be a two stage rebound setup. That's what the "flipped" part does.
    I had one of the early RP23 aftermarket shocks and it didn't have the second rebound stage. It was tuned for medium compression and rebound.

    The RP2 that came on my Specialized Pitch has the second stage. I think that shock was tuned medium compression, light rebound. The RP2 looked the same internally as the RP23 except for the extra rebound circuit and the propedal needle didn't have the intermediate positions.

    I think the additional rebound stage and the number of disc springs in the HSC valve is how Fox gets their different tunes for the shock.

    It's been a while since I had either shock apart and they're both retired but do those HSR ports look normal or are they awfully small?

  2. #52
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    Quote Originally Posted by HHMTB
    By the way, since I don't think anyone else addressed it in this thread, you CAN easily adjust the IFP chamber size in an inline shock. Just take out the valve core and add some oil. I've been doing this for a few years now and not only does it increase your tuning options, it also helps with IFP seal life since both sides of the seal are now lubricated with oil.

    Go easy on adding the oil. Like ~5-10 drops of oil at a time. Small changes here make big changes to the progressivity and you don't want to hydro-lock the shock.
    If you make the IFP chamber smaller to make the shock progressive, the pressure at full compression will be higher. Seems to me the IFP pressure and the damper oil pressure should be equal, but is there any operating condition where the seals or piston could be damaged? Is there an upper limit to IFP pressure? Any drawbacks to damper performance?

  3. #53
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    Yep, TNC, that's a two stage compression. With ProPedal on, the little shaft plunger closes off the shaft end bolt and compression flow only goes through the Bellevilles. With PP off, flow goes through the center of the shaft bolt through the side ports of the bolt and through the pyramid shim stack.

    I too am not a fan of the feel of the RP23's stock. I think it simply can't flow enough oil through the center of the shaft bolt for the pyramid stack to dominate. That means the Belleville PP circuit would dominate which equals dooky performance. At least that's my opinion from looking into it more.

    Now I didn't bother to undo the shaft bolt on the Monarch when I rebuilt it, but I would expect at the most there's only a dished piston or preloaded shim stack. It was pretty basic in appearance and that's why I didn't bother to take it all apart. Not that "basic" is bad, mind you, I like stuff that is simple and bulletproof, but I just didn't think I'd learn anything from taking it apart. Maybe the next time I open the Monarch I'll do that.

    For ARC, I haven't yet run into the upper pressure limit, but I assume there must be one. I will say I've gone as high as 300psi in a Roco LO DC, which probably means it was upwards of 400 at bottom out, without issue.

    Where the limit is would be a function of how good the shaft seal and shaft-to-guide bushing fit are. I.E. rudimentary O-ring will likely blow faster whereas a honest to goodness directional lip seal ought to seal harder as the pressure gets higher. Again, just my thinking. You may be able to feel more stiction as pressures go up because of the lip seal thing, but the swept area is small so probably not.
    "Adventure begins where good judgment ends."

  4. #54
    TNC
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    HH, on the possible inability to flow enough oil, maybe it's something like you encounter in some dirt motor shocks. Race Tech has made a ton of money with their Gold Valve system which flows more oil more effectively through the shim stack of many shocks. It was a dramatic improvement on my Kawasaki dirt bike with a KYB shock. Many compression pistons/valve don't flow enough oil to give optimum performance through the shim stack. I wonder if PUSH replaces the main piston along with shim stack modification to achieve what seems to be real performance increases on the RP series?

  5. #55
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    An appropriate comparison. From what I've heard, Push and Race Tech founders are friends, or at the very least know each other well. Hearsay, I know, but it makes sense if true.

    I know that the original generations of Push upgrade occurred when Propedal made its entrance ~2003 and the upgrade included a High Flow Piston to facilitate better tuning resolution.

    I don't know what goes into RP23's now (and keep in mind the one I show dissected is an 08, not the current Curnutt Boost Valve versions) but their website says they install the "VxRII High Flow Piston." I can only assume that they do this to remove the Belleville's and replace them with preloaded shims so as to create a better PP transition?

    If anyone wants to donate a Pushed RP23, I'll be happy to find out...
    "Adventure begins where good judgment ends."

  6. #56
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    "Adventure begins where good judgment ends."

  7. #57
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    Great info, HH. I had no idea that PUSH was already pursuing the higher flow piston concept, but it's absolutely logical.

  8. #58
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    When Push started up there was a lot of internet chat going around, I recall reading somewhere that the Race Tech guy was a mentor for Push.

    If you look through Push's website there's pictures of shock internals. Seems the shocks always get new a piston with new shimmed LSC, HSC, and HSR. Its probably easier for them from a tuning standpoint, regardless of shock brand or model you can have the same size ports and IFP pressure. All you have to do then is match the shim stack to the application.

    In my experience with the RP2 and RP23, compression flow was not as big a problem as high speed rebound flow. I think mine were always packing down a bit and you ended up riding too much in the wrong part of travel. Also the rebound portion of a fast square edge hit was worse than the compression.

    I ended up drilling the HSR ports to .047, and tossing one of the disc springs. IFP was 2.13" and about 150psi before bleeding. Turns out the IFP was too big or not enough pressure, it blew through travel so fast I had to compensate with an extra 20psi in the air can. The ride was lively and smooth, didn't notice any compression spiking. Traction was outstanding, perfect for fast singletrack riding as long as you were careful to get your weight back fast on downhill turns and didn't do anything resembling a jump. The RP23 was my first attempt and that bike got retired. I tried putting a schraeder valve in the RP2, but the schreader got bent and pulled some threads out while riding.

    HHMTB, can you see any path for low speed rebound oil flow with propedal engaged? As I see it, the propedal plunger blocks it off to hold the bike at sag height to help manage bobbing. If the HSR circuit was more active it would reduce the propedal effect. I think propedal is active on compression and rebound, the HSR on the RP floats got constrained for that reason.

  9. #59
    arc
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    Quote Originally Posted by TNC
    Great info, HH. I had no idea that PUSH was already pursuing the higher flow piston concept, but it's absolutely logical.
    They've been pushing that since they started. Did you see this?

    http://www.pushindustries.com/2009/i...OTO%20Services

  10. #60
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    Quote Originally Posted by arc
    They've been pushing that since they started. Did you see this?

    http://www.pushindustries.com/2009/i...OTO%20Services
    Sometimes it's hard to tell the difference between marketing hyperbole and actual engineering. Darren's association with Paul Thede tells me he pursues the real deal...as well as the PUSH'd Fox RC I had done to my Nomad more than two years ago. Frankly it wasn't until I did the Race Tech revalve on my dirt motor shock myself last year, that I truly grasped how important the main piston flow design could be. I mean, you'd think these guys designing and building these shocks could get something as important as the main piston oil flow correct. I thought anything could be fixed with proper shimming...if it had shims, of course...but if the main piston flow is insufficient, the shim stack never achieves full performance. If KYB, Showa, and some others could screw up on the main piston oil flow in some applications, I can see how the MTB guys could follow suit. Anyway, it seems Darren follows a similar trend as Race Tech and some other moto suspension companies...OK, maybe nothing earth shattering here...but that gives me even more faith in PUSH's efforts.

    I had already done some fairly extensive shock and fork servicing such as oil change, o-ring, piston ring, and main seal repairs. I had even experimented, somewhat successfully, with IFP position to manipulate travel characteristics. However, it wasn't until I did that Race Tech revalve on my own for my moto fork and shock that I really got the "full" picture.

  11. #61
    arc
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    Quote Originally Posted by TNC
    Sometimes it's hard to tell the difference between marketing hyperbole and actual engineering.
    Didn't mean for my comment to be taken that way. Perhaps I should have used the word advertising instead of pushing. No knocking Darren Murphy from me. I've learned a lot reading his posts, and its easier for me to attempt some shock tuning knowing that if I screw it up badly I can always send it to Push.

    The high flow piston has been there from the beginning. Push has always followed Race Tech's approach, custom high flow piston and shim stacks. I thought since you ride dirt bikes, you'd find Push getting into moto tuning interesting.

  12. #62
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    Hi, ARC. I think you are right that the LSR port of the shaft bolt gets closed when PP is switched on. However, I think that's why the second stage rebound circuit exists. The flutes and cross drills on the bolt itself allow flow through the second stage.

    Will it be different from the rebound with PP off? Absolutely. So your observation looks right to me: PP affects both compression and rebound.

    TNC: I agree, it makes way more sense to have excessive flow that you can choose to block off with shims than to never be able to achieve enough flow. Like most things in life, it's better to have too much and be able to say "no," than to hunger for more and not be able to get it... food, money, sex, etc
    "Adventure begins where good judgment ends."

  13. #63
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    I wanted to amend something I said back in December. I rebuilt a Roco Air R shock recently and came to a "no duh" realization. This shock had a big air bubble in it. The last time I rebuilt it, I put 140psi in the piggyback and 145 in the air chamber. The "no duh" part is that in an air shock it's the air chamber that acts against the main shaft seal and not atmospheric pressure. So having the air spring set higher than the IFP will allow air in past the main seal causing the big bubble effect.

    So my comment above saying I consider minimum IFP pressure to be 100psi does not apply to air shocks. Always set the IFP higher than your air chamber pressure will ever reach. As the IFP pressure raises much more quickly during compression than the main air chamber, I don't think a huge differential is needed. I've rebuilt with IFP at 170, air can at 140 and all seems well for the last few weeks.

    Sorry if I screwed anyone up in my prior post.
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  14. #64
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    Good thread. I still don't see how the IFP pressure affects anything other than effective total spring rate in the Monarch or Pre Boost Valve RP shocks. There is nothing "pressure" sensitive in the damping, it is all velocity or flow sensitive. I can see how a smaller IFP volume or higher pressure will cause the pressure to ramp up on compression, but couldn't you acheive the same boost by shimming the air can or more air pressure?

    The new BV RP23 should be a different animal, and I suspect they are very sensitive to IFP pressure.

    Could someone elaborate on how the rebound circuit is affected by PP position on RP shocks? I have not been happy at all with the rebound (or compression) on my 2011 RP23 BV, and I always run PP off on my Mach 5. Could I see an improvement in rebound damping with PP on? The bike always kicks me going over dips and g-outs even set to full slow rebound. I've switched to a Monarch Plus which is a million times better, but would like to now how to achieve better performance with the RP shock.

  15. #65
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    In my experience, changes to IFP pressure and, more importantly, position have a drastic effect on the shape of the spring curve that is harder to achieve than just by altering the volume of the air can. Basically, if you want minute changes to spring progressivity, yes, what you said is true. However if you need a lot more or a lot less bottom out resistance (especially in a non-position sensitive shock) your options are to re-shim, change oil viscosity, or alter the IFP pressure/position.

    This, by the way, is indictive of what I think are two schools of thought in suspension. On one end are people that don't like a lot of damping and rather depend on spring rate and shape to control bottom out and attitude. On the other end are people who tend to have softer, more linear spring rates and depend on more sophisticated damping to provide bottom out and attitude control. In my opinion, this was the difference between Marzocchi and Fox products. For me, I'm in the first group so being able to tweak IFP becomes quite important.

    I haven't taken apart a position sensitive RP23 yet as I'm still waiting for someone to donate one . I would venture to guess that the fact you can't get the feel you want no matter what your rebound setting is indicates that it's not the rebound that's the problem. My reason for generally not preferring fox air shocks is that to me they feel overly compression damped even in the softest tune. Further, DW bikes like yours work better with very little compression damping. Maybe in your particular situation it's just not able to use enough travel to adequately absorb the energy. Basically, you probably need a lighter compression revalve, or better yet, stick with your Monarch.

    To more directly answer your question, if the rebound circuit architecture in the current models is anything like the one I took apart and posted pictures of, turning on PP will turn off one of the rebound flow paths resulting in less rebound control (faster rebound). This correlates with what I've felt in the few RPs that I've ridden. It will also increase your low speed compression damping resulting in less trsvel used.

    Wanna donate your 2011 RP23 to me to experiment on?
    "Adventure begins where good judgment ends."

  16. #66
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    I have a rt3 with m/m on the can assuming it's a mid volume mid tune. With the ifp set at 250 it gets about 60% of it's full travel. set to 210 it's suppler and gets a little more travel but still not full travel.

    My bike has 3.5 inches of travel and a stroke of 38mm so it's leverage ratio is 2.3

    i guess i need a re tune or a lower leverage ratio shock.

  17. #67
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    Quote Originally Posted by HHMTB View Post
    Wanna donate your 2011 RP23 to me to experiment on?
    I'm super curious what's inside, but I'm thinking of getting the RP23 Pushed this winter (unless the aftermarket Monarch tuning finally arrives.)

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    bump

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    This thread is great - informative and motivating. In fact, it's motivated me enough to pick up the adapter valve to start messing with IFP pressure. But before I do, I want to make sure I understand the procedure.

    For the record, I have a Monarch Plus RC3 on a Trek Scratch. I spent a good amount of time on my '09 Commencal Meta 6 messing with Fox Float R air can volume using various plastic shims to get the best combination I was able of "proper" sag, big hit firmness and small hit compliance. It may not be perfect, but I like the feel better than that on my new ride, and I'm hoping I can make similar improvements on the Monarch.

    So I remove the IFP access cap with the Schrader core removing tool. I fit the adapter to the end of my shock pump, and thread this whole unit into the IFP valve. Do I empty the air from the air spring chamber first? Any other step I'm missing?

    I see Rock Shox specs 250 PSI for the IFP. There seems to be some debate about an ultimate lower limit - is there a consensus on a conservative lower limit? Is there a relationship between air spring pressure and IFP pressure, i.e. a ratio I should shoot for? Does IFP pressure affect sag?

    Thanks for any and all help,

    Forrest

  20. #70
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    Quote Originally Posted by vizsladog View Post
    I have a rt3 with m/m on the can assuming it's a mid volume mid tune. With the ifp set at 250 it gets about 60% of it's full travel. set to 210 it's suppler and gets a little more travel but still not full travel.

    My bike has 3.5 inches of travel and a stroke of 38mm so it's leverage ratio is 2.3

    i guess i need a re tune or a lower leverage ratio shock.
    My rt3 on a giant trance, tuned softer by a local tuner, with 200 lbs in the ifp chamber still won't get full travel unless pushed very hard on a cross country ride. It's harsh on compression even @ 35% sag. I gave up on it & had the stock float tuned by push, & the bike flows much better at the rear. I don't understand all the great praises for the monarch, perhaps for heavy weight riders on longer travel bikes?

  21. #71
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    Ok, I'll try to help. But please post anything new you learn so we all get better knowledge.

    Completely deflate the main air can. If there's any significant pressure in there and you let out all the IFP pressure, you'll get a big bubble in the oil as air forces its way around the main shaft seal. If after letting all the air out of the main air can, the shock compresses a little due to negative air spring interactions, it'd probably be best to unscrew the air can off the shock completely.

    Ok, so now you're ready to play with IFP. What you wrote, "So I remove the IFP access cap with the Schrader core removing tool. I fit the adapter to the end of my shock pump, and thread this whole unit into the IFP valve." is correct.

    I usually dump all the existing IFP pressure first just to make sure that that valve is still functioning. In the case of my report, it wasn't so I had to pull it out and clean crap off the sealing face. After you're satisfied that it's all mechanically in order, start pumping.

    As I mentioned in a post a short while back, set that IFP higher than your main can by some good amount. I used 30 or so psi greater, but you'll have to be the judge of your own comfort level. On a coil over, I'd say anything over 100 is good, but given an air shock, I'm staying above 170 psi on the IFP for this reason.

    Yes, IFP pressure affects sag to a small degree. However it affects mid stroke and bottom out more as does actual IFP volume. I can't point you to a magic ratio as it varies from shock model to shock model due to dimensional differences. Also, you may like something entirely different from what I like.

    Generally speaking, the higher the IFP pressure, the greater its effect on bottom out the more support you'll get mid stroke so you can lower the main air can pressure. It's a reasonable way to combat a wallowy shock up to a certain point. If you reach that limitation, you'll have to actually vary the IFP chamber volume. Less volume = more bottom out resistance/spring progressivity which can actually make the wallowing feeling worse in some cases.

    Anyway, that's all I got time for now. Post your findings please and we'll talk some more.
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  22. #72
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    OK, maybe I'll give it another shot.
    I thought I had read that 200 was the min. psi?
    You're saying I could drop it down to 170 lbs without any adverse affects?

  23. #73
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    Quote Originally Posted by kneecap View Post
    OK, maybe I'll give it another shot.
    I thought I had read that 200 was the min. psi?
    You're saying I could drop it down to 170 lbs without any adverse affects?
    He's saying that your IFP pressure ideally should be higher than your main chamber pressure, otherwise the air will migrate from the main chamber to the damping oil.

    You don't mention what your main chamber pressure is, so hard to tell what pressure will work for you.

    Try going down in decrements of 20psi. If you go too low, the shock will start fading due to cavitation. There are no adverse effects other than having to bleed the damper if you run it low in IFP pressure for short periods of time (I am NOT recommending it either!). It's long term operation in this mode that can damage seals and internals.

    Also, the shock will also have weaker mid-stroke and will be easier to bottom as you go down in pressure.
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    Make sure there is enough ifp pressure to keep the rebound side from cavitation on a fast hit. The easier the oil flows through the piston, the less ifp pressure needs to be on a coil shock. My swinger air shock can run as low as 50 lbs in the ifp. It uses an oring on the shaft and is not directional, so I'm not sold on the fact that the ifp needs to be higher than in the can on all air shocks. I do not know what type of shaft seal the Monarch uses. Just remember, the shock needs enough pressure in the ifp to get the oil through the piston without cavitation of the oil on the rebound side.

    Edit..late on my post I see...

  25. #75
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    Thanks warp, I think I have the main PSI set to around 100 lbs, (I'm 150 lbs suited up), so apparently I could drop the IFP down as low as 150 lbs if needed.
    I need a weaker midstroke & closer to bottom out would be fine.

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